1. Field of the Invention:
This invention relates to a lens barrel capable of performing both of manual operation and automatic operation by an electric motor.
2. Description of the Related Art:
Recently, in development of video cameras and still cameras, a type of camera having the AF function that performs focus adjustment automatically is taking the main stream. The electric motor is built into, for example, the lens barrel, when a lens system for focus adjustment is driven to effect focusing.
By the way, taking all shots by the automatic focusing operation gives no degree of freedom of making photographs. Also, in photographic conditions that hardly allow accurate automatic focus adjustment to occur, photographs of sharp focus cannot be made. From these accounts, there has been proposed a lens barrel which enables focus adjustment or the like to be carried out in either of the manual mode by the operator's hand and the automatic mode by the motor.
As lens barrels of such a type having both capabilities of manual and automatic modes, there are Japanese Laid-Open Utility Model Application No. Sho 57-54116, and U.S. Pat. Nos. 4,575,210 and 4,796,045.
Since, in the lens barrels of the aforesaid Japanese Laid-Open Utility Model Application No. Sho 57-54116 and U.S. Pat. No. 4,575,210, however, selection of the automatic focus adjustment and the manual focus adjustment is made by using manually operated changeover means, necessities arise that, for the changing over purposes, a clutch mechanism, a switch and other members be employed. This leads to an increase in the complexity of structure of the lens barrel. Thus, the prior art has a difficult problem on mechanisms. As to manageability, too, in some cases, for example, a case where after a shot by the automatic focus adjustment mode, the photographer wants to take the next shot with focusing correction by manual adjustment, another case where he desires to intentionally alter the focusing to a different object distance from that determined by the automatic focus adjustment, and yet another case where as a situation in which the automatic focus adjustment is difficult to do accurately is encountered, the camera has to be switched from the automatic focus adjustment mode to the manual mode, because any of these cases requires the photographer to actuate the changeover means for transition from the automatic mode of focus adjustment to the manual mode, quick selective setting cannot be done in any way. Hence, there are occasions for missing good shutter chances.
Also, in U.S. Pat. No. 4,796,045, the operating mechanism for the optical system is made with inclusion of means for combining a driving torque which comes from the manually operated actuator and another driving torque which comes from the electric motor in the form of a differential gear mechanism.
The operating mechanism of this type, however, because of using the differential gear mechanism in the driving torque composing means, suffers backlash owing to the gears in mesh. Hence, there is a problem that fine focus adjustment is hardly done in the manual mode.